PETpla.net Insider 09 / 2014

PREFORM PRODUCTION 35 PET planet insider Vol. 15 No. 09/14 www.petpla.net Two-stage Process Injection Moulding, part 14 Preforms for Single – and Two-stage Processing Preforms for these two processes are quite different, and one made for one process will not work in the other. The reason for this becomes clear when we look at what is actually happening to the preform just prior to stretch blow moulding. PETplanet insider is publishing extracts from successive chapters of Ottmar Brandau’s “Bottles, Preforms and Clo- sures”, which was first published by hbmedia. A newly revised version is reissued under the Elsevier imprint. Two-stage process injection moulding To guarantee optimal flow of the moulten PET into the injection cavi- ties, designers use ratios of gate wall thickness to body wall thickness. Ide- ally, one would want to keep the gate wall thickness as low as possible as this part of the preform does not gen- erally participate to a large degree in the stretching process and stays as an often wasteful, thick disc in the centre of the bottle. (In CSD bottles however, a thick centre disc is required because a thinner, amorphous centre would not be able to withstand the considerable